Apparatus for connecting a Stirling engine driven alternator to an ac mains supply is disclosed in International Patent Application No. PCT/GB01/00840. FIG. 1 of that application is reproduced herein as FIG. 1 and shows a linear alternator 10 that is driven by a Stirling engine (not shown). The mains supply is shown at 20 between neutral 21 and live 22. The alternator 10 is connected between neutral 21 and live 22 through two parallel paths 30 and 40. The first electrical path 30 has a switch 31 and a meter 32 in series. The second electrical path 40 has a first impedance 41, a second impedance 42, a switch 43 and a meter 44 connected in series in that order. A line 50 extends between impedances 41 and 42 to connect to neutral 21 via two switches 51 and 52.
In order to connect the alternator 10 to the mains supply 20, the Stirling engine must first be initiated to reach a threshold temperature before the alternator 10 may be connected to the main electricity supply 20 to initiate the piston of the Stirling engine. Connection to the mains supply 20 is achieved through a sequence of stages corresponding to various arrangements of the switches 31, 43, 51 and 52. In particular, the switch 43 allows the alternator 10 to be connected to the mains supply 20 initially through impedances 41 and 42 thereby limiting the current passing through the alternator 10. This ensures that an appropriate force is exerted on the piston of the Stirling engine to initiate its stroke, i.e. a sufficient force is provided to initiate the movement but that is not so large as to cause the piston to be driven into the walls of the piston chamber. The engine may then be connected directly to the mains supply 20 through path 30. The alternator 20 is disconnected from the mains supply only after the alternator 10 is stalled by placing impedance 41 across live 22 and neutral 21.
Whilst the above design works well, we have developed improvements thereto.